The majority of the known and commercially available low-pressure discharge lamps are so-called compact fluorescent lamps at present. These lamps are determined to replace incandescent lamps used in a wide field of industry and home applications. Main advantages of these lamps are low power consumption and a long lifetime. Disadvantageous is however in CFL-s their relatively high price and large length dimension. Many configurations have been proposed to solve the length dimension problem. Such solutions include the multiple tube arrangements and the coiled tube arrangements.
U.S. Pat. No. 4,527,089 discloses a compact fluorescent lamp (CFL) comprising multiple, individual tubes mechanically formed into an assembly and inserted into an outer envelope. The individual open-ended tubes are connected to each other through an arc directing means to form a continuous arc path. The outer envelope has a cylindrical shape, is hermetically sealed and includes an arc generating and sustaining medium such as an atmosphere of mercury and argon. The electric wires of the fluorescent lamp as lead-in wires are lead through a flare that serves as a sealing element of the cylindrical outer envelope. The ballast circuit providing energy for the fluorescent lamp is situated outside the outer envelope and therefore it requires special contact elements and arrangement.
U.S. Pat. No. 4,600,856 describes a compact low pressure arc discharge lamp with multiple tubes frictionally fitted into apertures in a base plate. The base plate is held in a fixed position inside the sealed outer envelope but there is no built in ballast in the outer envelope or bulb. A CFL of such a construction has to be connected to outer ballast, which requires external electric connections and a special connection means to connect the ballast to a power supply.
U.S. Pat. No. 6,064,155 discloses a fluorescent lamp with an outer envelope having an external shape of an incandescent lamp on a standard Edison-type base. The discharge tube is wound in a coil around the axis of the envelope and is disposed within the outer envelope. Ballast is also disposed within the outer envelope. A heat shield is disposed between the lamp and the ballast to thermally isolate the lamp from the ballast, whereby heat from the lamp will not adversely affect the ballast. Although this lamp is provided with integrated ballast inside the outer envelope, serious difficulties may arise during production due to the use of the heat shield disposed between the lamp and the ballast. It is not disclosed and therefore it is not clear from this document how the lamp and the ballast circuit is positioned and fixed inside the outer envelope and how the electrical connection between the lamp electrodes and the ballast circuit or between the ballast circuit and the base is established.
Accordingly, there is a need for a compact fluorescent lamp with integrated ballast inside the outer envelope and an improved configuration in order to make the lamp easier to manufacture and therefore to provide a CFL that is cheaper. There is also need for an improved method of production, which is easy to combine with the conventional manufacturing steps and therefore compatible with mass production. It is sought to provide a compact fluorescent lamp configuration, which readily supports different types of discharge tube configurations.